Current-limiting switching arrangements are configured, in particular, for interrupting current paths in the event of a short-circuit or of an overvoltage. Current-limiting switching arrangements of this type can also be configured single-poled or multi-poled, in particular three-poled. For each switching pole, they can have one or more switching contact pairs. In particular, these electrical switching arrangements are configured for switching off currents of more than 100 A, in particular, of several kA.
In the use, for example, of current-limiting switching devices, in particular current-limiting circuit breakers in the form, for example, of MCCBs (molded case circuit breakers) in extensively branched power distribution networks, selective staggering of the switching devices involved, using a minimum nominal current separation, is usual. Each branching level can be protected against any overload or short-circuits occurring, depending on the consumer devices connected, using a correspondingly dimensioned switching device.
For example, a switching device which is arranged adjacent to a consumer, often designated a “consumer-local” or downstream switching device, is configured for the smallest nominal current. If a short-circuit current flows both through the consumer-local switching device and through a switching device which is arranged, in the hierarchy of the power distribution network, above the consumer-local switching device, often designated a “consumer-remote” or upstream switching device, then only the consumer-local switching device is to shut down. In other words, in the event of a fault (short-circuit), only the switching device which is closest to the event is to interrupt the current flow.
The switching contact pairs of the consumer-local and of the consumer-remote switching device strike an electric arc on opening, wherein the opening width of the switching contact pairs and the arc energy are greater in the case of the consumer-local switching device due to the lower moment of inertia of the movable current path thereof including the switching contacts. This opening which may, under certain circumstances, be only single-poled must follow an all-pole shutdown of the consumer-local switching device. The consumer-remote switching device must not shut down, in order not to separate other consumers from the power supply network. The consumer-remote switching device may, however, act supportively by brief lifting of the switching contacts, for example, contribute to the shutdown of the consumer-local switching device by current limiting.
Switching devices which act in such a staggered manner in power distribution networks act selectively. In order to achieve this selectivity, it is necessary that the switching devices closest to the fault interrupt the current paths of all the switching poles more rapidly than the higher-level switching devices.
Generic releases and switching arrangements with releases of this type which are suitable for such rapid interruption of current paths are known, for example, from the German translation DE 691 10 540 T2 of the European patent specification EP 0 455 564 B1 and from the German translation DE 692 17 441 T2 of the European patent specification EP 0 538 149 B1.
The cited documents DE 691 10 540 T2 and DE 692 17 441 T2 each show, in particular, an electrical switching arrangement in the form of a circuit breaker with an insulating material housing which, for each switching pole, comprises two switching contacts pressed, in the switched on condition, against one another by spring force. The switching contacts can be separated by the effect of electrodynamic recoil forces if the current flowing through the switching contacts exceeds a predetermined threshold value, in order to bring about a limitation of the current. The circuit breaker comprises an overload and/or short-circuit detection member to send a signal, in the event of a fault, to a shutdown mechanism effecting the automatic shutdown of the circuit breaker. The circuit breaker also comprises an actuating element which responds to an excess pressure generated in the separating zone of the switching contacts by an electric arc struck in the event of electrodynamic recoil of the switching contacts, in order to actuate the shutdown mechanism of the circuit breaker. The actuating member is a gas-tight unit which is exclusively connected to the separating zone of the switching contacts and comprises a movable element, for example, a piston or a membrane with a limited control travel.
Applied to the movable element is firstly the excess pressure and secondly, by way of a retrieving apparatus, a suitable effective force. The displacement of the movable element causes the release of the shutdown mechanism of the circuit breaker, wherein the retrieving apparatus is dimensioned with a suitable effective force such that unintentional release in the event of simple overload or the response of a downstream current-limiting circuit breaker is prevented.
The shutdown mechanism of the circuit breaker shown can also be released both by the overload and/or short-circuit detecting element as well as by the actuating element which acts independently thereof. The release criterion made use of is the excess pressure generated when the electric arc is struck and which is in direct relationship to the arc energy. In other words, the pressure increases with increasing arc energy. Therefore, by evaluating the excess pressure, energy-selective shutdown of the circuit breaker is possible, wherein the energy-selectiveness represents a type of selectivity used particularly in low voltage power supply networks for shutdown in the event of a short-circuit, as described in the document “Energetische Selektivität in Niederspannungsnetzen” [Energy-selectivity in low voltage power supply networks], Schneider Electric, Technical volume No. 167, published May 1994.
Other releases of this type and circuit breakers of this type are known from the documents U.S. Pat. No. 3,631,369 A and EP 1 266 387 B1 and DE 100 13 161 B4. These each include an actuating element in the form of a lever which forms a blocking surface in a gas discharge channel for actuating a shutdown mechanism. The actuating member is deflected by a gas stream which flows into the gas discharge channel as a result of an excess pressure generated by the electric arc.